A group of scientists and academics today condemns as undemocratic and possibly illegal the government's plans to force through a new generation of nuclear power stations to meet Britain's energy needs for the next 30 years.

They warn that questions about the risks from radiation, disposal of nuclear waste and vulnerability to a terrorist attack have not been addressed - even though the government was ordered last February to repeat a public consultation on energy supply, after its exercise was declared unlawful by a high court judge.

Today the nuclear consultation group, made up of 17 energy economists and several of the government's independent advisers on nuclear waste, condemned the methods used in the second attempt to gather public and expert opinion.

"We are profoundly concerned that the government's approach was designed to provide particular and limiting answers," said Paul Dorfman, a spokesman for the independent group, which includes professors of Oxford, Sussex, and Lancaster universities, and Rutgers in the US. "Those answers risk locking in UK energy to an inflexible and vulnerable pathway that will prove unsustainable," he added.

In an 87-page report, the group says: "Significant issues were not consulted on in any meaningful way or resolved in practice. It has left the government vulnerable to legal challenge and may lead to hostility and mistrust of any future energy decision," the paper warns.

Contributors include Andy Stirling, director of science at the Science Policy Research Unit, Jerome Ravetz, fellow of the Institute for Science and Civilisation at Oxford, Dave Elliott, co-director of energy and research at the Open University, Gordon Walker, chair of environment at Lancaster University, and Frank Barnaby, at the Oxford Research Group.

The report comes as the government prepares to give the go-ahead next week for a major expansion of nuclear power, which could herald the building 20 reactors by private firms. Prime minister Gordon Brown is convinced, as was Tony Blair, nuclear power is needed to ensure energy security and to limit carbon emissions.

The intervention could trigger fresh legal action, however. Yesterday Greenpeace, whose challenge to the energy review was upheld last year, said it would wait to see the government's formal response on Tuesday before deciding whether to return to the courts. A new court case could delay the start of building stations by a further year.

The government is expected to insist it has a mandate. In meetings in the autumn, more than 1,000 people were asked their view of nuclear power after seeing videos and taking part in discussion: 44% said power firms should have the option to build nuclear; 36% said no.

A Department for Business and Enterprise spokeswoman said: "We gave people five months to respond, longer than the average three to four month consultation period. We have received 2,700 responses from the extensive consultation, which included public meetings across the UK, a written consultation document, and a website. Time is pressing. We need to make a decision on whether we should continue to get some of our electricity from nuclear, which is a low carbon form of making energy."

Green groups said the questions were loaded and the information presented biased and inaccurate. A complaint was made to the Market Research Standards Board alleging the market research firm involved broke the code of conduct.

A Greenpeace letter sent to the Treasury solicitors before Christmas says: "It would be unlawful for the government to make a decision to build new nuclear power stations without knowing what will happen to the new radioactive waste."

The consultation response will be a statement by energy secretary John Hutton, followed in days by an energy bill.